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		<h1 id="0007-button-release--reorganizing-the-code">0007: Button Release &amp; Reorganizing the Code</h1>

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		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/002_button/button_05_release.d" target="_blank">here</a>.
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<p>We’ll be making small but significant changes to the code this time around. The last time we looked at buttons, (<a href="./0004-oop-button.html">Post 0004</a>) we built everything from within the <code class="language-plaintext highlighter-rouge">main()</code> function. Further, we used the <code class="language-plaintext highlighter-rouge">onClicked</code> signal to get our button to do something.</p>

<p>This time around, we’ll be building the button from within the test rig class so all we have to do in <code class="language-plaintext highlighter-rouge">main()</code> is create the test rig window and everything else will be done automatically.</p>

<h2 id="changes-in-main">Changes in main()</h2>

<p>Take a look at the main function:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">void</span> <span class="n">main</span><span class="p">(</span><span class="nb">string</span><span class="p">[]</span> <span class="n">args</span><span class="p">)</span>
<span class="p">{</span>
	<span class="n">Main</span><span class="p">.</span><span class="n">init</span><span class="p">(</span><span class="n">args</span><span class="p">);</span>
	<span class="n">TestRigWindow</span> <span class="n">myTestRig</span> <span class="p">=</span> <span class="k">new</span> <span class="n">TestRigWindow</span><span class="p">();</span>
	
	<span class="c1">// give control over to gtkD.</span>
	<span class="n">Main</span><span class="p">.</span><span class="n">run</span><span class="p">();</span>
	
<span class="p">}</span> <span class="c1">// main()</span>
</code></pre></div></div>

<p>Previously, the window’s title was defined at the top of <code class="language-plaintext highlighter-rouge">main()</code> and passed in as a string variable rather than a string. This time, there’s no window title because—in the interests of going full-on OOP—it’s been moved inside the <code class="language-plaintext highlighter-rouge">TestRigWindow</code> class.</p>

<p>And you may also notice that we don’t even do a <code class="language-plaintext highlighter-rouge">testRigWindow.showAll()</code> here. It, too, has been moved inside the <code class="language-plaintext highlighter-rouge">TestRigWindow</code> class.</p>

<h2 id="changes-in-the-testrigwindow-class">Changes in the TestRigWindow Class</h2>

<p>And if all you looked at was the <code class="language-plaintext highlighter-rouge">main()</code> function, you might be led to believe this example didn’t do much. So, now let’s look at the <code class="language-plaintext highlighter-rouge">TestRigWindow</code> class:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">class</span> <span class="n">TestRigWindow</span> <span class="p">:</span> <span class="n">MainWindow</span>
<span class="p">{</span>
	<span class="nb">string</span> <span class="n">windowTitle</span> <span class="p">=</span> <span class="s">"Test Rig"</span><span class="p">;</span>
	<span class="nb">string</span> <span class="n">departingMessage</span> <span class="p">=</span> <span class="s">"Bye."</span><span class="p">;</span>
	
	<span class="k">this</span><span class="p">(</span><span class="cm">/* NO ARGS */</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="c1">// window</span>
		<span class="k">super</span><span class="p">(</span><span class="n">windowTitle</span><span class="p">);</span>
		<span class="n">addOnDestroy</span><span class="p">(</span><span class="k">delegate</span> <span class="kt">void</span><span class="p">(</span><span class="n">Widget</span> <span class="n">w</span><span class="p">)</span> <span class="p">{</span> <span class="n">quitApp</span><span class="p">();</span> <span class="p">}</span> <span class="p">);</span>
		
		<span class="c1">// a button that does something</span>
		<span class="n">MyButton</span> <span class="n">myButt</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyButton</span><span class="p">(</span><span class="n">buttonCaption</span><span class="p">);</span>
		<span class="n">add</span><span class="p">(</span><span class="n">myButt</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// this()</span>
	
	
	<span class="kt">void</span> <span class="n">quitApp</span><span class="p">()</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="n">departingMessage</span><span class="p">);</span>
		<span class="n">Main</span><span class="p">.</span><span class="n">quit</span><span class="p">();</span>
		
	<span class="p">}</span> <span class="c1">// quitApp()</span>

<span class="p">}</span> <span class="c1">// class myAppWindow</span>
</code></pre></div></div>

<p>These changes are all about maximizing OOP-ness and to that end, anything that has to do with a particular object has been moved into the class definition for that object. That’s why the missing window title shows up here as class data along with a <code class="language-plaintext highlighter-rouge">partingMessage</code> variable. Keeping all this where it’s easily found is a good habit to get into.</p>

<p>Now the constructor. Previously, all we did in there was call the parent using the <code class="language-plaintext highlighter-rouge">super()</code> function and then we hooked up the window’s close button. This time around, there are three major changes to the constructor:</p>

<ul>
  <li>there are no arguments because we’ve stored the window title as class data,</li>
  <li>we’ve gone back to a syntax for the <code class="language-plaintext highlighter-rouge">addOnDestroy()</code> function that we used in earlier examples, and</li>
  <li>the button is added here instead of in <code class="language-plaintext highlighter-rouge">main()</code>.</li>
</ul>

<p>So now all operations appear in the most appropriate places:</p>

<ul>
  <li><code class="language-plaintext highlighter-rouge">main()</code> encompasses all top-level calls, no more, no less,</li>
  <li>the <code class="language-plaintext highlighter-rouge">TestRigWindow</code> class contains all data and functions associated with it, no more, no less, and</li>
  <li>(when we get to it) it’s same for the <code class="language-plaintext highlighter-rouge">MyButton</code> class.</li>
</ul>

<h3 id="different-signal-for-the-windows-close-button">Different Signal for the Window’s Close Button</h3>

<p>We saw this approach to hooking up the close button back in the first blog entry and I talked about it a bit in <a href="./0001-imperative-test-rig.html">blog entry #0001</a>. It’s used here simply to keep us (me, mostly) from falling into a rut and as a reminder of how using it means defining the callback in a slightly different way. (Hint: look at the <code class="language-plaintext highlighter-rouge">quitApp()</code> definition with an eye toward counting arguments.)</p>

<h3 id="initializing-the-button">Initializing the Button</h3>

<p>And of course, the button is created here. Let’s move on.</p>

<h2 id="the-mybutton-class">The MyButton Class</h2>

<p>Here we go:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">class</span> <span class="n">MyButton</span> <span class="p">:</span> <span class="n">Button</span>
<span class="p">{</span>
	<span class="nb">string</span> <span class="n">buttonText</span> <span class="p">=</span> <span class="s">"My Butt"</span><span class="p">;</span>
	<span class="nb">string</span> <span class="n">actionMessage</span> <span class="p">=</span> <span class="s">"Action was taken."</span><span class="p">;</span>
	
	<span class="k">this</span><span class="p">()</span>
	<span class="p">{</span>
		<span class="k">super</span><span class="p">(</span><span class="n">buttonText</span><span class="p">);</span>
		<span class="n">addOnButtonRelease</span><span class="p">(&amp;</span><span class="n">takeAction</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// this()</span>
	
	
	<span class="kt">bool</span> <span class="n">takeAction</span><span class="p">(</span><span class="n">Event</span> <span class="n">event</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">widget</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="n">actionMessage</span><span class="p">);</span>
		
		<span class="k">return</span><span class="p">(</span><span class="kc">false</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// takeAction()</span>
	
<span class="p">}</span> <span class="c1">// class MyButton</span>
</code></pre></div></div>

<p>As mentioned above, there’s the data right at the top. And looking at the constructor, there’s a different signal being hooked up here, <code class="language-plaintext highlighter-rouge">onButtonRelease</code>. It doesn’t seem like that big a change until you look at the callback definition.</p>

<p>The callback now has two arguments, an event and a widget. Remember that widget is the base class for everything from windows to containers to buttons, so what we’re really saying here is: whatever widget-derived entity we happen to be pressing into service.</p>

<p>The event argument gives us access to a bunch of interesting stuff, but since the word count is already getting up there, we’ll talk about that in a later post. For now, just know there’s more than one signal we can handle with a callback and if we need access to the raw event that triggers the callback, that’ll be possible, too.</p>

<h2 id="conclusion">Conclusion</h2>

<p>Here we are at the end of another post. We covered a few interesting things here like reorganizing the code in a full-blown OOP style, hooking up a new signal, and reorganizing the code. Now I realize that points one and three are the same, but they’re so important, I mentioned them twice (paraphrasing a joke from Red Dwarf).</p>

<p>And that’s all for now. Be with them widgets and happy D-coding.</p>

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